Light-source units of the type including a light source that generates monochromatic light, such as an LED or a semiconductor laser, and also including a wavelength conversion element that converts the wavelength of the monochromatic light from the light source, such as a phosphor, are known (e.g., see Patent Literature 1). Since wavelength-converted light generated by the wavelength conversion unit is radiated in all directions from the wavelength conversion unit, it is necessary to take some measures in order to increase the output of the light-source unit. According to Patent Literature 1, as an attempt to increase the output of a light-source unit, a reflector is disposed behind a wavelength conversion unit, and light that is scattered backward from the wavelength conversion unit is converged at the wavelength conversion unit by the reflector so as to overlap light that is scattered forward.
Since the light generated by the light-source unit according to Patent Literature 1 has a divergent angle of 180°, the etendue is large. The etendue is defined as π×the light-emission area×NA2. In the case where light having a large etendue is supplied to an optical element having a small etendue, only a portion of the light is supplied to the optical element.